In such a way area called the furnaces including a toroidal chamber with the bottom wall rotating as to the rest of the chamber, the so said rotating hearth, being positioned several burners on the side walls and the ceiling wall of the furnace. The hearth, made of a thick layer of refractory material, is normally supported by a frame on which can be assembled the wheels cooperating with suitable tracks; alternatively, the frame has the circular tracks for the sliding and/or driving wheels of the hearth itself, placed on the ground.
The positioning on the ground of said wheels offers many advantages both from a practical point of view, such as the plant embodiment more easiness and the better maintenance possibilities, and from an economical point of view, bound substantially to the construction simplifications. Nevertheless, this kind of solution subjects the hearth refrac-tory material layer to considerable stresses, which can cause even substantial damages.